This invention relates generally to the field of assembly and test of electronic or optical components, such as integrated optical devices, and in particular to the coupling of light to planar optical waveguides.
The assembly and test of devices, such as integrated optical devices, require accurate alignment of components. For example, the assembly process for coupling optical fibers to optical chip components requires mechanical positioning to within 1 micron or less. The mechanical repeatability of chip placement equipment or manual loading of an optical chip into a test and assembly station is much greater than 1 micron. Thus the position of the optical waveguide within a chip with respect to the mating fibers is known to an accuracy of no better than several microns. Consequently, additional steps must be taken to locate the waveguide within this window of uncertainty.
When coupling light to and receiving light from a planar optical device, a light emitting optical fiber probe is coupled to a waveguide on the device. Light travels through the waveguide and is received by another optical fiber probe or array of probes on the other side of the waveguide. In most applications, the locations of the optical fiber probes and the device itself are not known accurately enough to allow for successful coupling based on mechanical repeatability of the system.
One prior approach is the use of a microscope together with manual positioning of the components. This approach requires trained and skilled operators. This is expensive and is subject to human error.
Another approach is the use of video microscopes in combination with image processing software and computer control of the positioning device. The equipment required typically includes two digital cameras, objective lenses, illumination equipment, an image processing acquisition system and processing software to interpret the image. This type of equipment is expensive and relatively slow, and measurement accuracy is limited to a few microns.
Moreover, the equipment used in these approaches tends to obstruct other processing equipment required to complete the assembly and test processes.
Accordingly, there is an unmet need in the art for a method and a system capable of finding the location of a waveguide in planar optical device that is both accurate and amenable to automation.
The invention relates generally to a system and method for finding the position of a waveguide in a planar optical device and has application to the coupling of light to a planar optical waveguide without connectors. The system comprises input and output optical fiber probes, a light source, a light detector or photodetector such as a large area photodiode and an optical power meter such as a photodiode power meter. According to the method the light detector is positioned at the exit of the optical waveguide of interest. Typically, the position of the waveguide is known to be within some window of uncertainty. Preferably, the area of the photodetector, which may be a large area photodiode, is large enough that the exit of the waveguide can be assumed to lie within the detection area of the light detector. The input optical fiber probe is coupled to the light source and is moved across the uncertainty window of the entry to the waveguide. The light transmitted through the device to the photodetector is measured and used to find the position of the entry to the waveguide. The input optical fiber probe is then positioned at the entry to the waveguide. The output optical fiber probe, which is coupled to an optical power meter, is used to scan for the exit for the waveguide. The probes may be moved automatically or manually.